Manufacture of smokeless powders



Jan.7,1936. F.0LSEN Em. 2,027,114

MANUFACTURE OF SMOKELESS POWDERS Filed March l2, 1932 5 Sheets-Sheet 3sa; vE//r 203 9 ferm/fier jj sceaw Z2 Mel/Mik g3 SaeFAcE TREAT .Z 5 naz?Patented Jan. 7, 1936 UNITED STATES PATENT OFFICE MANUFACTURE OFSMOKELESS POWDEBS ration of Delaware Application March 12, 1932, SerialNo. 598,332

s2 claims.

This invention relates to the manufacture of explosives and moreparticularly to the manufacture of smokeless powders, such as thosehaving a base of nitrocellulose.

One of the objects of this invention is to provide a process whereby theoperations may be carried out in a manner so as to secure a superiorproduct irrespective (within limits) of the base or material employed,i. e. Whether, for instance, freshly prepared or unstable material ordeteriorated powder or stock.

Another object is tovprovide a process whereby, during the course ofoperations, the product is purified and stabilized; and whereby theincorporation of additional ingredients such as stabilizers andmodifying agents, such as deterrents or accelerators may be readilyeffected.

Another object is to provide a process whereby the production ofdesirable grains, and more particularly spherical grains is assured.

Another object is to provide a process whereby the procedure may becarried out to secure economy and safety of operation.

Another object is to produce a powder grain of desired form and moreparticularly spherical in form.

Another object is to provide a powder grain which has incorporatedtherewith or is surface treated with a modifying agent such as adeterrent or an accelerator.

Another object is to provide a powder charge in which the several grainsare uniform as to their ignition characteristics or rates of combustion.

Further objects will appear from the detail description in which will beset forth a number of embodiments of this invention; it is to beunderstood, however, that the embodiments described are illustrativeonly of various embodiments of which this invention is susceptible. Inthe following description, as far as possible, an explanation will begiven of what believed to be the action taking place from a theoreticalstandpoint; it is to be understood, however, that in giving suchexplanation the theory and explanation is advanced for the purpose offacilitating an understanding from a theoretical standpoint; and it isunderstood that this invention is not to be limited toany advancedtheory or explanation from a theoretical standpoint.

In accordance with this invention the operations are so carried out asto produce grains which are uniform as to shape and preferablyspherical, and to an extent the process can be controlled so as tosecure uniformity as to grain size. Generally stated the desiredformation of the grains is accomplished by dispersing globules of thebase (such as nitrocellulose) in a medium so as to secure the formationof grains of the desired shape and more particularly of spherical form.This is accomplished in accordance with the embodiments of this inven'tion hereafter more fully described, by subjecting the base and asolvent to agitation in a nonsolvent medium (such as water) so as toproduce globules which are distributed in the medium and these globulesare individually consolidated so as to form grains which are spherical.To effect this purpose, there may be employed, a volatile solvent which,after performing its solvent action with the attendant production ofglobules, is vaporized by heating the medium to the vaporizing point ofthe solvent, the medium being not only a non-solvent, but alsorelatively non-volatile at the temperatures employed.

In order to effect efllcient distribution. the process is carried on inthe presence of what is hereafter descriptively referred to as aprotective colloid, and which is believed to perform the function ofeiecting a quasi-emulsion between the base and solvent and thenon-solvent medium, with the base and solvent as the internal phase.

The production of globules, or the production of the quasi-emulsion maybe secured in various ways. Thus in accordance with one embodiment ofthis invention, the base is dissolved in a Vsolvent and the colloidalsolution or lacquer is agitated rather violently in a non-solventvehicle in the presence of the protective colloid to form the globules.In accordance with another embodiment of this invention, the base isagitated with a solvent distributed in the non-solvent vehicle so as toform an emulsion with the medium as the internal phase; uponthe additionof the protectivev colloid the emulsion is broken and under agitationreformed, or as we may say. inverted with the' medium as the externalphase. In accordance with still another embodiment of this invention,rather large particles of the base are agitated with a solventdistributed in the non-solvent vehicle in the presence of the protectivecolloid so as to form the globules as the base particles are attacked orsoftened by the solvent. In all cases,` globules are distributedthroughout the medium. and these globules are then subjected totreatment to extract the solvent, as by distillation of the solventsecured by heating the medium to near the vaporizing point of thesolvent, or therebeyond.

'I'he distillation is sc carried out as to eifect a gradual vaporizationof the solvent from the several globules; the process is preferablycarried out by effecting vaporization at a rate decreasing from thebeginning to the end of the vaporization period and at a rate less thanthe rate of diffusion of the solvent from the interiors to the exteriorsof the globules. Such a distillation secures -a solid grain asdistinguished from one which is hollow and porous.

The process is subject to control so as to predetermine the size of thegrains. accomplished by controlling the extent or violence of theagitation of which the grain size is a function; by controlling theamount of the protective colloid present, of which' the grain size isalso a function; or by controlling the viscosity of the dissolved orpartially dissolved, base of which the grain sizevis also a function. Bycontrolling these various factors, the grain size may be controlled andpredetermined after establishing limits based upon experimental data.

In accordance with this invention, a stabilizer, and even a neutralizeris incorporated with the grain and distributed throughout the grain.This is accomplished in accordance with the various embodiments of theinvention by, for instance, incorporating the stabilizer with a solventand a base to form a lacquer where the base is dissolved prior to itsbeing emulsied with the vehicle or medium; by incorporating thestabilizer in the solvent which is then distributed in the medium orvehicle and thereafter agitated with the base; or by incorporating thestabilizer with a solvent, distributing the same in the medium andsubjecting rather large particles of the base to agitation in themedium. 1n the various embodiments, the stabilizer is not only uniformlydistributed throughout the globuies formed within the medium and thegrains thereafter formed from the giobules, but any acidic ordeteriorated elements present will be distributed throughout the vehicleor medium. The neutralizer is added to the medium and similarlydistributed so as to perform its useful function.

The modifying `agent such as a deterrentor accelerator may beincorporated with a grain and distributed throughout the grain in amanner similar to that of incorporating the stabilizer previouslyreferred to, by incorporating the modifying agent with a solvent, as bydissolving the same in the solvent, when it will be carried through theprocess as previously described in connection with the stabilizer.

After formation of the globules in the medium or vehicle as heretoforedescribed, and. after distillation of the solvent from the severalglobules to form the grains, the medium is permitted to cool to atemperature suciently low to permit any modifying agent or stabilizerdissolved in the normally non-solvent medium to separate out at thelower temperature. In the case of the modifying agent, such as adeterrent, it will become deposited on the grains 4so as to provide asurface treatment inthe formof a coating or impregnation. t

After cooling of the medium, and when the grains have becomeconsolidated or hardened, they may be subjected to a screeningoperation. This can be a wet screen process in which the oversizes canbe sent back for reworking and the screened grains can be subjected to awringing operation and thereafter to a drying opera- This .can be tion.The solvent which has been vaporized can be recovered in a suitablesolvent recovery apmay, however, be surface treated prior to drying witha suitable modifying agent, such as a deterrent or an accelerator. Theymay be then dried and glazed in the usual manner and thereafter blendedif desired.

Inv accordance with an embodiment of 'this invention, a powder chargecan be produced in which the grains have the same rates of burning. Thismay be accomplished, by screening the grains by a series of screeningoperations, so as to secure a powder charge having grains ofsubstantially the same size, as well as shape. This is possible due tothe fact that the grains are spherical as distinguished from angular oroblong. A powder charge comprising portions of normally diiferent ratesof burning, as by being composed of even spherical grains of differentsizes, may be treated so as to have the same rate of burning. This maybe accomplished by treating portions having a higher rate of burningwith a deterrent, by treating portions having a lower rate of burningwith an accelerator, or by f treating two portions respectively with adeterrent and an accelerator, so as to secure a blended charge in whichthe grains have the same rate of burning. Q

A number of embodiments of this invention heretofore generally referredto will now be described under the descriptive headings; I. A Solutionor lacquer process"; II. Distributed solvent process; III. "Large baseparticle process; it will be understood,'however. that these headingsare simply for classification purposes and are not limitative. Theseembodiments will be described in connection with the accompanyingdrawings, in which:

Figure 1 is a diagram illustrating classiiication I; i

Figure 2 is a section showing a detail of what may be called the still,while Figure 3 is a diagram showing the relation of the stator androtor; i

Figure 4 is a diagram illustrating classification II; and

Figure 5 is a diagram illustrating classification In the diagrams,Figures 1, 4 and 5, apparatus parts are shown which may notl beessential for the `practice ofthe processes hereinafter described; thatis done for the purpose of facilitating` the disclosure of the processesand in order to diagrammatically illustrate the steps or operationsofthe process. As will, however, hereafter appear, a number of operationsor steps may be performed in the same container, such as the still withits agitator.

y I. Solution or lacquer process vIn thisfembodiment, the base may be4nitrocellulose which as to kind and character, as well as composition,may be varied; it may be wholly or partially purified brousnitrocellulose in the form of nitrated flakes, linters. or wood pulp;

u may be dense colloided nitrocellulose in the form of existing powder,whether fresh or deteriorated, or of good, poor or indifferentstability; it may be nitrocellulosef-rom other processes such as dustand mud or bulk powder and cannon powder. The nitrocellulose may be ofany suitable degree of nitration such as having a nitrogen content of12.4 to 13.4.

The modifying agent employed, and to be incorporated with the powdergrain may be any suitable deterrent such as dinitrotoluene,diamylphthalate or dibutylphthalate. Where DNT is employed itspercentage can vary from 10% to 20% relative the weight of the powder.

The solvent employed may be any suitable solvent such as ethyl acetate,but any other suitable solvents of nitrocellulose may be employed. Whereethyl acetate is employed in this particular embodiment, it is used inthe proportions of ve parts to one part of the powder grain.

Any suitable stabilizer such as dlphenylamine may be employed in theproportion of 1% of the weight of the powder.

A suitable neutralizer is calcium carbonate (CaCOa) in the form ofpurified prepared chalk which is employed in the proportions of 1%relative the weight of the powder.

A suitable protective colloid is starch in the form of corn starch inthe proportion of 2% of the weight of the water used as a medium orvehicle. It is prepared by boiling so as to produce a gel. It ispreferably of a form which has been prepared by the acid process havinga pH value of 5., an acidity value of .085 and an ash content of .12.Other suitable agents for performing the same function may, however, beemployed, such as gum arabic, dextrin or bentonite.

The medium or vehicle is preferably a nonsolvent such as water, having arelatively high boiling point and non-inammable. It is employed in thisembodiment in the proportion of eight times the weight of the powder. Upto the distillation process it can be used at ordinary temperatures,that is from 10 to 20 C.

Referring -now to Figure 1, the nitrocellulose base. the deterrent, thesolvent and the stabilizer may be mixed in a vessel I to produce alacquer. This lacquer may contain from 15% to 25% dissolvednitrocellulose and can have a viscosity of from 300 to 2500 seconds(Falling Ball method) at 25 C.

The neutralizer, the colloid and the vehicle i may be placed in a vessel2, it being preferable that the starch be previously formed into a gelby boiling in a small quantity of water, and when added to the eightparts of water there is formed a thin colloidal solution. The vessel 2may, however, be dispensed with and the calcium carbonate, starch andwater may be mixed directly in the vessel 3 hereafter referred to as thestill. Into this vessel, the'lacquer is later conducted.

This still comprises a casing of suitable capacity, closed at the topexcept for an inlet opening provided with a closure; it is also providedwith a discharge opening 4, provided with a closure. It has arrangedtherein a stator provided with stationary vanes 5 and a rotor providedwith blades 6 so as to form what is known as a turbine mixer. The rotormay be driven through a shaft 1 from a suitable source of power. Arelation of 'stator and rotor blades which is particularly suitable isshown in Figures 3 and 4. While the stator blade 5 is shown assubstantially radial, the rotor blade 6 is shaped as shown along acurvewith a terminal extending in practically a-radial direction. Withsuch .aconstruction the liquid vthrown out by cen- When the contents of thestill, including the calcium carbonate, the starch and the water is inviolent agitation, the lacquer is conducted into the vortex formed,thereby forming a quasiemulsion with the lacquer as the internal phase.After the globules have been properly formed, steam is applied to thecoil 8 while the agitation is slowed down thereby causing the solvent tovaporize and pass to the recovery apparatus 9. After volatilization ofthe solvent the contents of the still are allowed to cool to atemperature of about 50 C. The contents of the still are now passed onto a screen I I, from which the oversize is sent back for reworking,while the screened material ls sent to a suitable centrifugal wringerI2. It will be understood that the screen II may be of a construction so'as to size the material into one or more sizes with the oversize, aswell as the very fine material, sent back for reworking. From thewringer the powder grains may be surface treated at I3. They may then besent to a suitable drying apparatus I4, a glazing apparatus I5, and ablending apparatus I6.

Operation Upon the addition of the lacquer to the vessel 3 containingthe water. starch and calcium carbonate under agitation, the lacquer isbroken up into globules so as to produce a quasi-emulsion with thelacquer as the internal phase. The formation of the globules and thedispersion of the same throughout the medium is facilitated by the factthat the liquid is projected by the rotor blades against the statorblades.

In the formation of the globules from the lacquer, various emulsionphenomena are encountered. While the system,nitrocellulose-solvent-water, tends toward a condition of emulsioncorresponding to water-lacquer emulsion with the lacquer as the externalphase, this tendency is overcome by the presence of the starch,particularly in the presence of a neutralizing agent such as calciumcarbonate, tending to produce an alkaline material. While the actioncannot be determined with certainty, it is believed to be connected withsurface tension, differential viscosity and adsorption. By GibbsTheorem, if a substance lowers the surface tension of water whendissolved in it, that substance will concentrate at interfaces,producing what is termed adsorption. If a substance produces a viscoussolution with water, then the -water solution will be most viscous nearasurface. If Va condition has been produced where the emulsion will beone in which the lacquer i`s the internal phase, as globules or dropletsof lacquer are detached by the agitator the colloid becomes adsorbedaround each droplet, producing a protected globule. The most viscouslayer will be adjacent the droplet and there will exist a gradient ofdiminishing viscosity from the surface of the droplet to the main bodyof the water phase.

The way in which the adsorbed film protects two globules from coalescingis believed to be somewhat as follows:-When the medium containing theglobules is placed in motion, movement will take place along the planeof least viscosity, which is the plane between the two globules; even iftwo globules are moving directly toward each other, they will movearound each `other without touching o r coalescing, since movementalways takes place along planes of least viscosity. After formation andprotection of the globules, the system hasv a strong tendency towards acondition of minimum surface energy. If

it were possible, coalescence would take Aplace to satisfy thecondition. Because of this tendency, the globules of lacquer assume theshape which offers least interface, namely spherical.

The size of the globules and of the grains thereafter formed dependsupon a number of factors, namely, the grain size decreases with increaseof rotor speed, decreases with increase of percentage of the colloid anddecreases (within limits) with decrease of inherent viscosity of thenitrocellulose, that is viscosity of a given Weight of nitrocellulose ina given quantity of a standard solvent. The grain size also seems toincrease (within limits) with decrease of percentage of the solvent.

The distillation procedure operates to remove the solvent; in thisprocedure, however, care must be taken not to remove the solvent at toohigh a rate, for otherwise hollow and porous grains having theappearance of popcornand a corresponding low density will result. If,however, the solvent is evaporated at aslow rate and at a temperaturebelow the boiling point of the solvent, extremely dense spheres willresult. The time required for this is however, protracted and mayinvolve a production' problem. Advantage can, therefore, be taken of anumber of vfactors including the lower boiling point of a solvent inWater emulsion.

Experience has shown that in removing solvent from a lacquer globule,the rate at which solvent can diiuse through the lacquer depends uponviscosity and, therefore, upon the amount of solvent present in thegrain. The rate of diffusion must` exceed the rate of removal of thesolvent or a hard case or skin is formed around the globule which doesnot thereafter soften and the grain formed shows that shrinkage of thenitrocellulose upon theinner face of this case has taken place so as toform a hollow shell. One of the problems is, therefore, the removal ofthe solvent at a proper rate to produce solid as distinguished fromhollow and porous shells. In accordance with this invention the removalof the solvent is so controlled that the solvent is removed at a rapidrate at the beginning and thereafter at a decreased rate until the grainbecomes case hardened. After case hardening, the solvent can be removedat a reasonable rate without appreciably affecting the density. As apractical illustration, during the case-hardening period, distillationis started at a temperature of 68 C., and the heat is so maintained thatover a period of 65 minutes, the temperature will rise to 72 C. y Thisis really a distillation at a decreased rate, for at a uniform rate `thetemperature at the end of the casehardening period would be much higherthan '72 C.; accordingly, although the temperature may, therefore, rise,the distillation is reallyrat a decreased rate. After suchcase-hardening period, the temperaturecan be raised to C. until thesolvent has been expelled.

During the distillation period, the contents of the still are kept inagitation, although the agitation need not be as violent as during theformation of the globules. At the end of the distillation period thecontents of the still are allowed to cool to about 50 C. as previouslydescribed and at this temperature such of the modifying agent (such asDNT) as is in the water is deposited on the grains so as to form in`effect a coating.

II. Distributed solvent process The materials employed are generally thesame as in Process I heretofore described, except that the relation ofthe solvent to nitrocellulose can be decreased to a point 4 to 1 andeven to a point 2.5 to 1. The process is generally as follows:

Referring to Figure .4, the deterrent, solvent and stabilizer can bemixed in a vessel I0, while the calcium carbonate and the water can bemixed in a vessel 20 and the contents of both can be then mixed in avessel 2|. The contents of vessel 2| can then be passed to a vessel 22into which the nitrocellulose is discharged, and the contents of 22 cannally be discharged into avessel 30 which may again be a. still providedwith an agitator 23 and a'steam coil 8. The agitator may, however, be ofthe simple paddle form and need not be of the turbine mixer form. Itwill be understood that the nitrocellulose, deterrent, solvent,stabilizer, calcium carbonate, and the water vessel 30 may be otherwiseof the form shown in Figure 2, may have an outlet discharge on to thescreen I-I, and a vapor outlet to the solvent recovery apparatus 9.

Assuming the materials (other than the starch) to be mixed in the vessel30, it being here noted that the amount of water is 11/2 times theweight of the nitrocellulose, agitation is proceeded with until notonly'the nitrocellulose, deterrent and stabilizer have become dissolved,but until a portion of the water has been emulsied with the lacquer.This results in an emulsion with Water as the internal phase and theresultant lacquer as the external phase, although the lacquer phase maynot be completely continuous. Agitation can now be stopped to allow theemulsion to settle out from the unemulsied water and consolidat in onelarge piece of emulsion instead of several pieces. 'I'he temperature inthis case is preferably maintained at about 50 C.

The starch prepared as previously described .in connection with ProcessI so as to form a gel,

is now added to the still and 6 parts of water compared to the Weight ofthe nitrocellulose added; or the starch gel is previously mixed with the6 parts of lWater and added to the vessel 30;

this is preferably done while the contents of the vessel-are inagitation. Upon the addition of the colloid, the emulsion previouslyformed is broken and inverted so as to produce a quasi-emulsion with thewater as the external phase and with the lacquer as the internal phaseso as to again distribute globules of the base-solvent, etc., throughoutthe medium or vehicle. Distillation, cooling, screening, etc., can thenbe proceeded with as previously described in connection with Process I.

This process has an advantage `over Process I in thatit is not necessaryto preliminarily dissolve the nitrocellulose in the solvent, but thesolvent is distributed throughout the vehicle or medium and attackingthe nitrocellulose dissolves the same. The proportion of solvent canaccordingly be loweredrto 4 to 1 and even to 21/2 to 1 as distinguishedfrom 5 to 1. The production of spherical grains is again secured as inProcess I and again nitrocellulose in any suitable form as ymay beinitially mixed in the vessel 30. The i in Process I can be employed,the temperature previous to distillation is in this process raised to 50C. so as to clect more efficient and rapid solution of thenitrocellulose, the solution period being 2-4 hours in case cannonpowdes used as a base.

III. Large base particle process The materials for this process are thesame as in Processes I and II previously described, except that it isonly practical to employ large grains, particularly of dense colloidnitrocellulose, an example of which is deterioratedcannon powder. It isnot practical to employ fine grained powder. The ratio of solvent topowder can be 4toland even3to1.

The deterrent, solvent and the stabilizezariM be mixed in a vessel (Flg.5) calcium carbonate, starch and water can bemixed in a vessel 200 withabout 7l/2 parts of water, compared with the weight of thenitrocellulose, the starch being prepared as previously described inconnection with Process I. The nitrocellulose and the contents of vessel200 can then be mixed in a vessel 20| and the contents of the latterdischarged into the vessel 30, which may be of the same construction asdescribed in connection with Process 1I and which may have a vaporoutlet to the solvent recovery apparatus 9, and may lead to the materialoutlet on the screen l I as previously described. It is understood,however, that the nitrocellulose, calcium carbonate, starch and watermay be mixed in vessel 30. While the mass is in agitation, the contentsof vessel Illll may be added to the vessel 30 or all of the materialsmay be added to vessel 30 and mixed therein.

In the vessel 30, agitation is carried on for a period of about twohours at about 20 C., which is the normal temperature of the water asobtained from the supply. 'I'his results in the formation of globulesdistributed throughout the medium or vehicle. At the completion of thisperiod distillation is proceeded with as described in Processes I andII, the contents of the vessel allowed to cool and the materialscreened, wrung, dried. etc., as previously described.

While the formation of globules may be accomplished by the solventaction of the solvent distributed throughout the medium and attackingthe nitrocellulose, the action is believed to be somewhat asfollows:-The water and solvent form an emulsion comprising droplets ofsolvent in the water. These droplets attack the nitrocellulose grainspromoting softening, as well as swelling of the same. The violence ofthe agitation causes portions of the gelatinlzed portions of thenitrocellulose to be removed yfrom the grains so as to assume globularform in the water medium. The violence of agitation. the ratio ofsolvent to nitrocellulose, and the ratio of water to nitrocelluloseagain influences the size of the particles formed, so that theproduction of uniform 4spherical grains Vof rpredetermined granulationcan be produced. Variations ir'i gravimetric density and in granulationcan be affected by appropriate changes in the above mentioned factors.

The starch plays an important part in this process, for when it isemployed, as previously described, spherical grains are produced, exceptfor small angular grains which seem to be the residue of the originalgrains of nitrocellulose and which can beldiscarded byv screening. If nostarch is used, then flaky grains are produced. The process has theadvantage that the period be injurious.

required for the formation of the globules is two hours as compared tofourteen hours required in Process I when ordinary cannon powder isused.

As previously stated, such colloids `as gum arabic, dextrin or bentonitemay be used. Where gum arabic is used it may be employed in theprcportion of 1% relative the weight of the wa er.

Incorporation of stabilizer and neutraliser nylamine are acidic, and inlarge quantities such as are present in one of these spots may beantagonistic toward nitrocellulose. Various decomposition products suchas ether peroxide formed by oxidation of the residual ether, ethylnitrate formed by alcoholysis of the nitrocellulose by the residualalcohol, and the possible presence of cellulose nitrite would helpexplain the unstable character of some cannon powders.

In accordance with this invention, as described in the variousembodiments, the nitrocellulose, even if deteriorated is puried andstabilized. That is particularlyv true where the nitrocellulose isactually dissolved as in the Processes I and II and even in Process IIIwhere the nitrocellulose is partially dissolved and at least gelatinizedBy this action the nitric acid present in the spots is liberated andspread uniformly throughout the solution. This is important since asmall amount of acid uniformly distributed through nitrocellulose mightnot be harmful, whereas this same quantity of acid when locallyconcentrated would The acidic nitrated diphenylamines are also broughtinto homogenous solution. and diphenylamine which could not be reachedby the nitric acid is brought into intimate contact therewith. Morediphenylamine is usually added to the solution as a further safeguard.

When the dissolved, or partially dissolved or gelatinized nitrocelluloseis mixed intimately with water containing calcium carbonate, aciddiffuses out into the water and is neutralized. 'Ihis alkaline mediumalso has a hydrolyzing action upon any unstable esters which may bepresent and the solvent action of the water frees the solution of etherperoxide if such is present.

A mild alkaline material like calcium carbonate was chosen for thefollowing reasonsz--When calcium carbonate is suspended in water some ofit dissolves setting up the following equilibrium:

The concentration of OH ion is large enough to `neutralize acids (whichshifts the equilibrium to the right) but not large enough to injure thenitrocellulose. As soon as some of the OH ions are neutralized, moreundissolved calcium cartion is afforded by emulsifying some of the watercontaining calcium carbonate within the lacquer solution, thenitrocellulose acting in this instance as the emulsifying agent. Thisemulsion is later broken by the colloid present in the remaining part ofthe water and the phases reversed to form globules of lacquer in water.

Incorporation of modifier In accordance with this invention, asillustrated in the various embodiments, the modifying agent such as adeterrent is uniformly distributed throughout the grain.v This iseiiiciently accomplished in the embodimentl described vby dissolving thedeterrent in ethyl acetate which, in addition to being a solvent fornitrocellulose is also a solvent for DNT. In Process I this modifier isdistributed throughout the lacquer, and this is also true in ProcessIIWhere the modifying agent is again distributed throughout theglobules. This is even `true of Process III where the modifying agentagain enters the nitrocellulose with the solvent. l

Upon vaporization of the solvent, the modifyagent is left in the grain,except such parts as may dissolve in the water at the distillationtemperature. Upon cooling of thewater, however, it separates from thewater and coats or impregnates the grains.

Grain formation As previously described, the powder produced is not onlysubstantially spherical in` shape but uniformly dense. It, therefore,has advantages not only from a ballistic standpoint but also from aloading v standpoint. Spherical grains of the same size and compositionburn at the same rates. Accordingly by screening grains closely the samesize can be secured. 'Ihat is impossible with angular or oblong grainswhich, on account of their varying shapes have different volumes, eventhough all may pass through the same screen opening. In accordance withthis invention there is, therefore, produced, a powder chargein whichthe various grains of the charge have the same rate of burning and eventhe same igniting characteristics.

From a loading standpoint the spherical grain shape and the ability toreadily screen to the angular grains where the weight per volume dependsupon the arrangement of the grains in the charge.A Spherical grains alsoow easily.

'I'he powder presents a wide range of possibilities since it can beprepared from a mixture of nitrocellulose having dierent potentials anddifferent degrees of nitration; furthermore, by the incorporation ofmodifiers such as deterrents and accelerators, the ballisticcharacteristics may be varied particularly since they can be uniformlyincorporated. These also serve to improve the gel structure andresistance to moisture.

The uniformity of grain size, shape and composition of the powderembodying thisinvention also has the following advantages over grainsprepared by cutting slices from an extruded cord, because it isimpossible to obtain the degree `of uniformity with the latter type thatis attained by the powder embodying this invention; for the mechanicalaberrations of the cutting equipment will be such that the slices arewedge shaped,

thereby producing an unevenness of web thickness that affects theuniformity of burning which is achieved by closely sized sphericalgrains.

Surface treating and blending The `powder grains embodying thisinvention can be surface treated with any suitable modifying agent suchas a deterrent or an accelerator. `An example of a deterrent is DNT,while an example o'f an accelerator is nitroglycerine. 'I'he surface`treatment may be performed in any suitable manner so as to secure thedesired ballistic.l results. In applying a deterrent such as DNT it maybe applied with any suitable emulsifying agent such as saponin in water,or the emulsion may be diluted and added to an agitating slurry of waterand the powder. In the application of an accelerator such asnitroglycerine, .it may be added to a water andpowder slurry in the formof an alcohol-benzol solution, the alcohol and benzol being evaporated.'I'he surface treated powder grains may be given a water-dry treatmentto insure a hard surface and to improve the flowing property of thegrains.

These grains may then be glazed in the usual way.

Powder of varied grain size may be blended to secure the desiredballistic properties. Grains of di'erent sizes may be treated to securethe same rates of burning; thus grains of larger size may be surfacetreated with an accelerator such as nitroglycerine; grains of smallersize may be surface treated with a deterrent such as DNT or grains oftwo sizes may be treated, one with an accelerator and the other with adeterrent s`o as rate of burning or improving the the ease of ignition.

In case coarse grained powder be coated with nitroglycerine and blendedwith the finer material, either uncoated or coated with DNT, im-

proved hygroscopicity and improved ignitibility will be secured throughthe use of portions of the nitroglycerine coated powder blended with theuncoated or DNT coated finer material.

Close control in granulation made possible by the spherical powderenables the load to be so designed that none of the particles aresufliciently large as to remain unburned. On the other hand, anadditional factorof safety is secured by only coating the screenedportion which is finer than the average, avoiding thereby the slowing ofthe particles of coarser granulation.v This conditon can be stillfurther enhanced when the larger particles are nitroglycerine-coated asthis tends not only to improve the ignitibility of these largerparticles, but also to increase their rate of burning.

It will be understood that while in the ernbodiments described, theexplosive or powder base has been nitrocellulose, various other powderand explosive bases may be employed to secure many of the advantages ofthis invention. It will also be understood that various combinations and'subcombinaitions maybe employed to secure many of the advantages ofthis invention without reference to other combinations andsubcombinations; that is contemplated by and within the scope of theappended claims. It will further be understood that various changes maybe made in details without departing from the spirit of this invention;it will, therefore, be understood that this invention is not to belimited to the various details described.

Having thus described the invention, what is claimed is:

1. In the art of making explosives, the process comprising, agitatingnitrocellulose and its solvent with an excess of a non-solvent in thepresence of a protective colloid and extracting the solvent.

2. In the art of making explosives, the process comprising, dissolvingnitrocellulose in a solvent, agitating the solution with an excess ofnon-solvent vehicle in the presence of a protective colloid andextracting the solvent during agitation.

3. In the art of making explosives, the process comprising, dissolving asmokeless'powder base in a volatile solvent, agitating the solution withan excess of a non-solvent vehicle in the presence of a protectivecolloid and heating the vehicle to the vaporizing point of the solventduring agitation.

4. In the art of making globular smokeless powder grains, the processcomprising, dissolving a smokeless powder base and a deterrent in asolvent, agitating the solution with a vehicle which is substantially anon-solvent for the base and solvent to an extent sulcient to formglobules and extracting the solvent from the globules.

5. In the art of making globular smokeless powder grains, the processcomprising, dissolving a smokeless powder base and a stabilizer in asolvent, agitating the solution with a vehicle which is non-solvent forthe base and solvent to an extent sumcient to form globules andextracting the solvent from the globules.

6. In the art of making explosives, the process comprising, agitatingnitrocellulose with a solvent distributed in a non-solvent vehicle andadding a protective colloid.

7. In the art of making explosives, the process comprising, agitatingnitrocellulose with a solvent distributed in a non-solvent vehicle toeffect solution of the nitrocellulose in the distributed solvent, addinga protective clloid and extracting the solvent.

8. In the art of making explosives, the process comprising, agitatingnitrocellulose with a volatile solvent distributed in a non-solventvehicle to eiect solution of the nitrocellulose in the distributedsolvent, adding a protective colloid and heating the vehicle to thevaporizing point of the solvent'.

9. In the art of making explosives, the process comprising, agitating asmokeless powder base with a deterrent and a solvent distributed in anexcess of a vehicle which is substantialiy immiscible with the solventto form globules of the base and the deterrent dissolved in the solventin the vehicle and heating the mixture to vaporize the solvent from theglobules.

10. In the art of making explosives. the process comprising, agitating asmokeless powder base with a stabilizer and a solvent distributed in avehicle which is substantially immiscible with the solvent to formglobules of the base, the stabilizer and the solvent in the vehicle andheating the mixture to vaporize the solvent from the globules.

11. In the art of making explosives, the process comprising, agitatingnitrocellulose with a solvent distributed in an excess o1 a non-solventvehicle in the presence of a protective colloid.

12. In the art of making explosives, the process comprising, agitatingnitrocellulose with a volatile solvent distributed in an excess of anonsolvent vehicle in the presence of a protective colloid and heatingthe vehicle to the vaporizing point of the solvent.

13. In the art of making explosives, the process comprising, agitatingnitrocellulose with a stabilizer and a solvent distributed in anon-solvent vehicle in the presence of a protective colloid.

14. In the art of making explosives, the process comprising, forming anddispersing globules of a smokeless powder base and a. volatile solventin a non-solvent medium and heating the medium to effect vaporization ofthe solvent from the globules at a rate decreasing from the beginning tothe end of the vaporization.

1 5. In the art of` making explosives, the process comprising, formingand dispersing globules oi a smokeless powder base andfa' volatilesolvent lin a non-solvent medium and heating the medium to eiectvaporization\ of the solvent` from the globules at a rate less than therate of diffusion of the solvent from the interiors to the exteriors ofthe globules.

16. In the art of making globular smokeless powder grains, the processcomprising, dissolving a smokeless powder base in a solvent,distributing a stabilizer throughout the dissolved base, forming thedissolved base into globules and extracting the solvent.

17. In the art of making globular smokeless powder grains, the processcomprising, dissolvingA a smokeless powder base in a substantiallynonwater-soluble solvent, distributing a deterrent throughout thedissolved base, forming the dissolved base into globules and extractingthe solvent.

18. In the art of making explosives, the process comprising, introducingnitrocellulose and a solvent into a non-solvent vehicle in the presenceo1' a protective colloid with attendant agitation to form grains andcontrolling the grain size by the amount of colloid present.

19. In the art of making explosives, the process comprising, forming anddispersing globules of nitrocellulose solution in an excess ofnon-solvent medium, and solldlfying the globules while in dispersion. 4

20. In the art of making explosives, the process comprising, agitatingnitrocellulose particles of substantial size in a non-solvent vehicle,bombarding the particles with globules of solvent. and f removing thesolvent.

2l. In the art of making explosives, the process comprising. agitating asmokeless powder base in a non-solvent vehicle with solvent which issubstantially immiscible with the vehicle, suilcient to form globules ofdissolved base, and thereafter removing the solvent from the globules.

22. In the art of making explosives, the process comprising, agitating asmokeless powder base with a solvent distributed in a non-solventvehicie to effect an emulsion, and adding a protective Y colloid to theemulsion.

23. In the art of making explosives, the process comprising. agitating asmokeless powder base with a solvent distributed in a non-solventvehicle to effect an emulsion, adding a protective colloid to theemulsion, and heating the vehicle to the vaporizing point of thesolvent.

24. In the art of making propellant powder grains, the processcomprising, forming a solution of nitrocellulose in a solvent which issubstantially immiscible with water and boils below the boiling point ofwater, the solvent employed being 2.5-6 l times the weight ofnitrocellulose, agitating the solution in 6 to 8 times its weight ofwater to form globules of nitrocellulose lacquer dispersed in the water,and heating the mixture to the vaporizing point of the solvent while theglobules are maintained in dispersion.

25. In the art of making globular smokeless powder grains, the processcomprising, dissolving a smokeless powder base in a volatile solvent,agitating the solution with a non-solvent vehicle to form globules anddistribute the same throughout the vehicle, and heating the vehicle tothe vaporizing point of the solvent while the distribution of theglobules is maintained.

26. In the art of making explosives, the process comprising, agitatingnitrocellulose with a volatile solvent distributed in a non-solventvehicle at normal atmospheric temperature to form globules in thevehicle, and thereafter heating the vehicle to the vaporizing point ofthe solvent while the distribution of the globules is maintained.

27. In the art of making explosives. the process comprising, dispersingglobules of a smokeless powder base and a volatile solvent in an excessof a non-solvent medium at substantially normal atmospheric temperature,and heating the medium to effect gradual vaporization of the solventfrom the globules while dispersed.

28. In the `art of making explosives, the process comprising, agitatingnitrocellulose with a deterrent and a solvent distributed in an excessof a non-solvent vehicle in the `presence of a protective colloid.

29. A propellant powder grain comprising, a solidiied droplet of agelatinized smokeless powder base, surface treated with a modifyingagent.

30. A propellant powder grain which is a solidifled droplet ofgelatinized smokeless powder base.

31. A propellant powder grain comprising a solidified droplet of agelatinized smokeless powder base surface treated with nitroglycerine.

32. A propellant powder grain comprising a solidied droplet of agelatim'zed smokeless powder base surface treated with a deterrent.

FREDRICH OLSEN. GORDON C. TIBBI'I'I'S. EDWARD B. W. KERONE.

